Yes, this is common slang for this type of t-shirt, but why perpetuate it? I would think that you, the instructor, being a woman, would be professional and refer to this t-shirt as it should be. Isn't it ironic that a man has to raise this point?
Nothing about women being beaten should be so casually referenced. Sexism and misogyny will never be overcome in our society as long as women continue to passively accept it in all forms, even the minor ones like this. It's the little things that make a difference for good and bad.
Unfortunate, since the video itself is useful otherwise.